patch 9.0.0259: crash with mouse click when not initialized

Problem:    Crash with mouse click when not initialized.
Solution:   Check TabPageIdxs[] is not NULL.

src/mouse.c

@@ -471,6 +471,8 @@ do_mouse(
 
     start_visual.lnum = 0;
 
+    if (TabPageIdxs != NULL)  // only when initialized
+    {
 	// Check for clicking in the tab page line.
 	if (mouse_row == 0 && firstwin->w_winrow > 0)
 	{
@@ -540,6 +542,7 @@ do_mouse(
 	    tabpage_move(c1 <= 0 ? 9999 : c1 - 1);
 	    return FALSE;
 	}
+    }
 
     // When 'mousemodel' is "popup" or "popup_setpos", translate mouse events:
     // right button up   -> pop-up menu

src/testdir/test_tabline.vim

@@ -147,4 +147,18 @@ func Test_tabline_20_format_items_no_overrun()
   set showtabline& tabline&
 endfunc
 
+func Test_mouse_click_in_tab()
+  " This used to crash because TabPageIdxs[] was not initialized
+  let lines =<< trim END
+      tabnew
+      set mouse=a
+      exe "norm \<LeftMouse>"
+  END
+  call writefile(lines, 'Xclickscript')
+  call RunVim([], [], "-e -s -S Xclickscript -c qa")
+
+  call delete('Xclickscript')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -731,6 +731,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    259,
 /**/
     258,
 /**/